The present invention is related to a polymer-based casing suitable for encasing cooked and uncooked sausage meats.
Artificial polymeric sausage casings must fulfill numerous requirements if they are to be suitable for commercial use. These requirements differ depending on the type of meats that are to be encased. For example, cooked meats, such as traditional sausages purchased from a grocery store, wieners, hams, salamis, and liver pates are inserted into a casing in an uncooked, paste-like form, and are then cooked or smoked in the casing. Depending on the particular market, this cooked meat product may be sold with or without the casing, and are oftentimes stored refrigerated below 4° C. Some of the requirements for these types of cooked meats are as follows:                1. Shirrabiltiy—The film must have the ability to be shirred and stay shirred until the filling process.        2. Recovery Power—The film must continue to cling without creasing when the previously heated packaged meat cools or loses weight due to evaporation of water.        3. Strength—The film must ensure that the high filling pressure mainly produces an elastic deformation of the tubular film, without localized bulging.        4. Peelability—The film must be easily removable from the packaged meat without damaging the meat product.        5. Temperature resistance—The film must be able to tolerate temperatures associated with the cooking process.        6. Barrier properties—The film must have good barrier properties against permeation of oxygen and water vapor.        
On the other hand, chorizo is a type of uncooked, ground fresh meat that is often mixed with vinegar and spices, and is stored at ambient temperatures such as 20-25° C. Unlike the cooked meats discussed above, chorizo and other similar products have a fermentation or curing process after production where moisture and CO2 gas are produced by the meat. Fermented meats and sausages are characterized by their tangy flavor and in most cases chewy texture. The characteristic tang results from bacterial fermentation during which lactic acid and other byproducts of fermentation accumulate. The pH of fermented sausages typically ranges from about 4.6 to about 5.3. Fermented sausages include both dry and semi-dry varieties. Representative fermented, dry sausages include Genoa salami, hard salami, and pepperoni. Representative fermented, semi-dry sausages include summer sausage, farmer sausage, and chorizo. The moisture and gas created during the curing process must be able to permeate through the casing film to avoid breaking or puncturing, and to avoid unwanted bacterial growth and acidity that would otherwise develop and damage the quality and taste of the meat.
Chorizo and other similar uncooked products are encased primarily with cellulosic casings, but are also produced using collagen casings or natural pork tripe. Tubular cellulosic casings are well known in the art of meat casings, and have been widely used for many years by numerous manufacturers for both cooked and uncooked meats. The basic process for manufacturing regenerated cellulosic casings is through the well-known viscose process, whereby a liquefied colloidal dispersion of cellulose fibers is created in an alkaline liquid carrier.
Once the cellulosic casing is formed, it is typically shirred according to well known methods wherein long tubular lengths, often called “strands” are compacted and pleated to provide shorter, coherent tubes, often called “shirred sticks” or “sticks.” High-speed shirring machines are common in the art, such as those disclosed in U.S. Pat. Nos. 2,984,574, 3,451,827, 3,454,981, 3,461,484, 3,988,804, and 4,818,551, which are incorporated by reference herein. The coherency of the shirred stick is important in order that it remain straight and rigid. Small diameter shirred food casings must be packaged for distribution and sale, and this packaging is critical to commercial performance since the casing has a thickness of from about 20 microns to about 40 microns, and is therefore prone to damage. Although the sticks must be rigid to prevent deformation and survive transportation to the foodstuff manufacturer, the sticks must also be easily dispensed without waste when being filled with meat paste using high speed filling machines.
Although the standard for chorizo production, cellulosic casings have several drawbacks. The most commercially important drawback is that cellulosic casings are too permeable to moisture. This allows loss of saleable product weight or sometimes the opposite problem—moisture can be absorbed into the cellulosic casing thereby allowing fungus to grow inside the casing. Also, when printed with more than two colors, ink tends to permeate through a cellulosic casing, thereby contacting and staining the product.
Another synthetic alternative for chorizo casings exists with biaxially stretch-oriented polyamide films. Polyamide, commonly called nylon, is a semi-crystalline thermoplastic that is composed of linear aliphatic segments that are connected by amide linkages. Polyamide can be produced either by the polymerization of a lactam and an amino acid or a dibasic acid and a diamine. The wide variety of routes by which polyamide can be produced make it possible to tailor the backbone to meet specific needs. The various types of polyamide are identified by number designations, which represent the number of carbon atoms in each of the starting materials. For example, nylon 6,6 is made from the 6-carbon hexamethylenediamine and a 6-carbon adipic acid. All nylons absorb moisture from the atmosphere, and the water that enters their structure causes dimensional changes and acts as a plasticizer. These factors must be taken into account when designing a product constructed of polyamide. Additionally, biaxial orientation—stretching the film in one direction and then at right angles—can be used to orient the crystals and make the film stronger. Polyamide is also inexpensive and has excellent tensile strength as compared to other polymers, which are reasons for its widespread use as a fiber. Unfilled polyamide is biologically inert, and most grades have been cleared for food contact use by the U.S. Food and Drug Administration.
In general, single-layer polyamide sausage casings are capable of easy integration into the shirring and filling operations that presently exist for cellulosic sausage casings. Although cheaper to manufacture than cellulosic casings, pure polyamide casings have several shortcomings as compared to traditional cellulosic casing technology, as applied to both cooked and uncooked sausage meats. For example, pure polyamide casings cannot be smoked, cannot be effectively peeled either manually or automatically, and do not allow gas to permeate for uncooked sausages that undergo fermentation.
For cooked meats, several layers of polyamides and other polymers are often used in order to compensate for certain disadvantageous properties of pure polyamide. For example, a number of different types of cooked meats and sausages require casing materials that exhibit low permeability to water vapor. The barrier against water vapor prevents weight loss due to evaporation of water from the contents, which reduces the saleable value of the product. This also ensures that the sausage casing surrounds the meat in a tight, crease-free manner, even after relatively long periods of storage without formation of hollow spaces between the inner wall of the casing and the sausage meat where jelly pockets can form. For this purpose, it is known to combine a polyamide layer with a second layer of a different polymer whose permeability to water vapor is lower than that of the polyamide layer. There are, however, certain types of meats where even the reduced permeability of this two-layer composite casing is too high to be suitable for use. For example, certain cooked meats severely discolor when exposed to even the slightest amount of oxygen. The prior art has resolved this problem by providing additional polymeric layers to the casing that provides superior oxygen barrier. As a result of these multiple layers, several other commercially important qualities are often sacrificed, such as the transparency of the casing, the printability of the casing, and consistency and operability during the shirring and filling processes. Accordingly, it is desirous to provide a new single-layered polymer-based casing that meets all of the above requirements for packaging cooked meats and sausages.
For uncooked meats, polyamide casings provide a different problem. As discussed above, chorizo and other uncooked products that require a curing/fermentation process (such as soft cheeses) require a casing that is permeable to the gases and moisture that are produced. Pure polyamide casings have inherently too high a barrier to gases and moisture for this particular application. As an alternative, several polyamide casing producers have attempted to blend polyamides with other polymers such as polyester, polypropylene, and Surlyn® to provide a permeable film. The problem with this approach is that the shirred stick that results from such films can be too rigid, and have problems with unshirring prior to usage. For these and other reasons, polyamide casings are not used today in the chorizo and uncooked sausage meat industry. For uncooked meats, what is needed is a single-layered polymer-based casing that can be tailored to meet both product permeability requirements as well as the commercial processing requirements for shirring and filling.